The present invention relates to a knee prosthesis, surgical procedure and apparatus designed for use as a system in revision surgery of previously performed knee arthroplasties. The prostheses and system of this invention may also find utility in the initial prosthetic replacement of a damaged or diseased knee joint.
Replacement of the femoral and tibial components of knee joints has become more common in recent years as a reconstructive practice for damaged and diseased joints. However, it is still considered that about 10 years is the expected life for prosthetic joint components. Accordingly, it is expected that joint implants will require replacement through a revision procedure.
Revision surgery is performed to correct failures of previously implanted knee prostheses. These failures occur for a number of reasons including malposition, loosening of the prosthesis, infection or dislocation. Such categories are not necessarily mutually exclusive since infection may cause a loosening of the prosthesis which, in turn, might cause dislocation.
When a knee must be replaced or a previously implanted prosthesis removed and a revision prosthesis inserted, it is often the case that additional bone has been removed or lost in the loosening or revision process. When this occurs, the interior portion of the femoral component of the prosthesis must be augmented to add additional thickness to compensate for the bone that has been lost or removed and stabilize the new prosthesis. In addition, the cuts that remove the extra bone must be correctly made relative to the femoral prosthesis, whether an original or revision implant, for accurate positioning in relation to a tibial component and the patella.
If the replacement is done as a staged procedure, there is an opportunity to obtain a mold of the bone ends and to custom manufacture a prosthesis for an accurate fit. Prostheses may also be custom manufactured based on information obtained through X-rays or other imaging systems. However, it is preferable to perform the joint replacement in a single surgical procedure. Furthermore, it is preferable to be able to obtain an optimum functioning knee prostheses for a wide range of patients with as few individual parts as possible. Also, it is desirable to have a system of prostheses constructed around a constant reference point which may be used in initial prosthetic replacement of the knee and in subsequent revision procedures, the constant reference point serving to simplify preparation of the implant site and provide uniformity within the system thereby simplifying the procedures.